Acid-Base Balance Flashcards
what is whole body pH governed by?
intracellular pH levels
what is normal plasma [H]?
40 nM
what is the main challenge of acid/base regulation in the body?
[H] must be kept very low, but it is produced at extremely high levels
what is the Henderson-Hasselbalch equation?
pH = pKa + log10[A-]/[HA]
undissociated (weak) acids can buffer strong bases, and their conjugate anions can buffer strong acids
ok
what is the effective range for a base?
+/- 1 pH from the pKa
what system is most responsible for the buffering capabilities of our body? why?
the Co2- bicarbonate system is responsible for 60% of our buffering capacity
even though carbonic acid’s pKa is ~2, it is more likely to dissociate into H2O and CO2. This means the rxn can be written as
CO2 + H2O H + HCO3
w/ its own equilibrium constant and pKa of 6.1
the CO2-bicarb buffering system has a pKa of 6.1 yet still acts as an effective buffer in our body. how?
the buffer exists in an open system where CO2 is free to leave, and the buffering power is proporitonal to [HCO3], which increases as pH increases
respiratory buffering
the lungs may eliminate (during acidosis) or retain (during alkalosis CO2 to assist the CO2/HCO3 buffering system
pCO2 remains constant
respiratory compensation
lungs change pCO2 via hyper or hypoventilation in an attempt to normalize blood pH
isohydric principle
all buffersin a compartment are in equilibrium w/ each other
this allows you to measure the status of 1 buffer and infer information about the others
HCO3 buffers both the ICF and ECF equally, but they contain different amounts of HCO3. how is this possible?
the ICF is twice as big as the ECF, but it has twice as much HCO3, meaning that they are effectively buffered equivalently.
where is phosphate an important buffer?
intracellularly
what is the important buffer in muscle?
creatine phosphate
describe bones as buffers
they will accept a H in exchange for K or Na. they contain HCO3 and CO3, as well as some crystalline alkaline salts. thus, they manage acidosis.
prolonged acidosis results in bone breakdown
describe urinary buffers
phosphate is important in the urine since HCO3 is completely reabsorbed. NH3/NH4 is also important
creatinine, citrate, urate
describe some metabolic processes that generate acids or bases
- the primary producer of acid is the metabolism of carbohydrates, fat, and amino acids to produce acidic CO2
carbs- lactic acid and CO2 (acidic)
fat- ketoacids and CO2 (acidic)
organic anions (basic)
amino acids- varys. breakdown of carboxyl (basic) neutralized by the breakdown of the amine (acidic). dibasic AAs produce acids and dicarboxylic AAs produce bases. these generally cancel, but sulfer AAs mean that amino acids are net acidic
organic phosphates- acidic
nucleic acids- acidic
divalent cations (basic) can often get caught in the gut, meaning that net intake becomes acidic
OVERALL- DIET RELATED BREAKDOWN IS ACIDIC
what are the limits on urine pH?
no lower than 4.5 and no higher than 8.5
how is bicarb reabsorbed in the proximal tubule?
80% of filtered bicarb is reabsorbed via two mechanisms
- Na/H exchange pumps H into the lumen, where it combines w/ bicarb to form carbonic acid, which is converted by carbonic anhydrase to H2O and CO2 which can passively cross the membrane, where it is reconverted by carbonic anhydrase to carbonic acid, which dissociates, and the bicarb leaves the cell via Na/3bicarb cotransporter
- everything is the same, but the initial H is pumped into the lumen using an ATPase